Modified starch containing drilling muds having a reduced filtration rate



Application September 16, 1955, Serial No. 534,877

16 Claims. or; 252-351 o Drawing.

"{I hQ present invention is directed to a suspension of finely,idivided solids in an aqueous medium for use in well drilling operations. More particularly, the invention is directed to a drilling mud having a low filtration rate. In its more specific aspects, the invention is directed to a drilling mud to which has been added materials for reducing filtration ratey The present invention may be briefly described'as in-, volving a drilling mud comprising at least percent by weight of finely divided solids in an aqueous saline me-' dium having dissolved therein about 2 to 15 weight percent of salt and to which has been added about 1 to 15 pounds of starch per 42 gallon barrel of mud and about 0.5 to 5 pounds per'42 gallon barrel of mud of an additive having an average molecular weight, of about 90 to3,000 and a ratio of carbon to oxygen of about 1.5 to 2.7, said additive being taken from the group consisting of alkoxy ethers of ethylene and propylene glycol, polyethylene'and polypropylene glycols, and alkoxy ethers of polyethylene and polypropylene glycols, said alkoxy radicals of said ethers containing not more than about 6 carbon atoms, said drilling mud containing not more than about 1 pound ofalkali metal hydroxide per 42 gallon barrel of mud. In the rotary method of drilling boreholes, an aqueous suspension of finely divided solids, commonly'referred to as a drilling mud, is pumped down the drillstem' through the openings in the drill bit and upwardly through the annular space between the drill stem and the Wall of the borehole to the surface of the earth. A primary purpose for employing the drilling mud is to pick upjthe cuttings produced by the drill bit and to transport these cuttings to the surface of the earth. The" drilling mud also serves other important functions such aslubricating thebit and'the drill stem, cooling the bit, and furnishing a hydrostatic pressure head toprevent flow into'the bore-' hole, of formationfluid, such as oil, gas, and water, from the various strata penetrated by the drill bit. In'certain cases it is highly desirable that the mud form athin,

difiicultly permeable coating or filter cake on the Walls of the borehole for the purpose of reducing loss of water from the borehole to the formation and thereby reducing softening of the borehole walls and cavinginto the drill hole. It is perferable that the filter cake formed 'on'the walls of the borehole be thin rather than thick so as to avoid mechanical difficulties in moving the bitinand out of the hole and in placing casing in the hole.

barytes, iron oxide, barium sulfate, calcium carbonate, silica, and the like are often added to such a suspension in order to increase its specific gravity. In many cases, however, the drilling fluid used in oil and gas wells may be obtainedby forming a suspension in Water of surface clay-at or adjacent the well site or may be prepared in the process of drilling by dispersing in water the cuttings produced from the borehole. Weighting materials,"clays,

Heavy materials such as Patented Mar; 19, i957 fi ce 2 and chemicals may, of course, be added to the drilling fluid prepared in the last mentioned manner. L i Almost any fluid will perform some of the-aforemen tioned functions, such, for example, as cooling the drill bit, but to perform some of the other functions, it is neeessary that the drilling fluid employed possess certain very definite properties. For example, a drilling mud may have suflicient gel strength to prevent s'ettling'of solids from the mud when circulation of the mud'is' stopped, but, at the same time, its other properties may be such as to result in the deposition of a thick filter cake on the borehole walls rather than the preferred thin cake. When large amounts of water filter from the mud into the formations surrounding the borehole, the solids content ofthe mud remains as a filter cake on the wall of the hole, reducing the size of the annular passage. Sloughing of such a thick filter cake or this together with caving of water-softened-borehole wall may cause the drill pipe to become stuck. On the other hand, the employment of a drilling fluid having a low filtration rate restricts to a relatively'small amount the waterthat can escape from the mud under the pressure differential prevailing in the borehole. A small loss of water from the mud to the formation means, of course, that only a thin filter cake will be deposited on the borehole walls. Use of the proper mudwillhelp to preserve the-borehole walls intact. i A

Occasionally, drilling mudswhich have a relatively low, filtration rate may be prepared from borehole cuts; however, it has generally been found necessary to incorporate filtration reducing agents into the mud to impart this de-,

object of thepresent invention is to providea method for reducing the loss of water from an aqueous saline dispersion orsuspension of finely divided solid material, An-. other object of thepresent invention is to provide a drillingfluid suitable foruse in; the rotary drilling of boreholes into subsurfaceformationsand having a low filtra-- tion rate. Another 'object'of thepresent invention; is to provide an agentwhich, on addition to the aqueous saline drilling fluid used in the drilling of boreholes'into subsurface formations, willsubstantially reduce the loss of water; therefrom by filtration; A further object of the present invention is to provide an agent which, on addition to a drilling fluid, will substantially reduce the loss of 'water'there from by filtration, but which will not increase excessively the viscosity of the fluid or substan-- tially affect its ability'to maintain solids in suspension. I

The method oft he present invention may be briefly described as involving the addition to a mixture, dis? persion, or suspension offinely divided solid, material-in an aqueous saline, liquid-vehicle having dissolved therein about 2 to 15 weight percent of salt, starch and an additivehaving an average molecular weight of about to 3,000 and a ratio of carbon to oxygen of about 1 .5 to 2.7, saidadditive being taken from the group consisting of alkoxy'ethers of ethylene and propylene glycol, poly;

ethylene and polypropyleneglycols, and alkoxyfethers of polyethylene and polypropylene glycols, said alkoxy radicals: ,of said ethers containing not more than about 6" carbon atoms, said drilling mudcontaining notmore. than about 1 pound of alkali metal hydroxide'per, 142;

gallon barrel of mud, and said additive being added in carbon tooxygen '(i. e., 1.5 to 2.7).

an amount sufircient to materially reduce the tendency of the mixture, dispersion or suspension to lose. water by filtration. The method of the present invention also comprises the maintenance of proper amounts of starch and additive in the drilling mud during drilling operations in order that the reduced tendency of thedrilling mud to lose water may be maintained. By applying the proper amounts of starch and additive, the water'lost by filtration fromthe dispersion or suspension is reduced to a low value.

' The composition of the present invention may be described briefiy as a mixture comprising an aqueous saline vehicle containing about 2 to weight percent of dissolved salt in which a finely divided solid material is dispersed or suspended and to which has been added starch and an additive having an average molecular weight of about 90 to 3,000 and a ratio of carbon to oxygen of about 1.5 to 2.7, said additive being taken from the group consisting of alkoxy ethers of ethylene and propylene glycol, polyethylene and polypropylene glycols, and alkoxy ethers of polyethylene and polypropylene glycols, said alkoxy radicals of said ethers containing not more than about 6 carbon atoms, said drilling mud containing not more than about 1 pound of alkali metal hydroxide per 42 gallon barrel of mud, said starch and additive having been added in an amount sufficient to substantially reduce the tendency of the composition to losewater by filtration.

The finely divided solid material of the composition of my invention may, of course, be any finely divided solid which is capable of being dispersed or suspended in an aqueous liquid vehicle,- and; an example of such a dispersion or suspension is the drilling fluid used in rotary drilling of boreholes, which may include various solid materials as hereinbefore indicated.

The finely divided solid material employed in the practice of the present invention will ordinarily include clay, such as colloidal clay bodies. For example, I may use in m'y drilling mud or aqueous suspension, colloidal clays, such as Wyomingbentonite, El Paso surface clay, medium-yield drilling clays from Texas, clays containing the montmorillonites and especially sodium'montmorillonite. The calcium-montmorillonite clays may be employed and clays containing other suitable cationic coinbinations of the montmorillonites may be used. Sodium montmorillonite such as that encountered in Wyoming bentonite is included in-the preferred type of clay. I also contemplate that I may use in the practice of my invention muds such as those produced when clayeysubsurface formations are drilled. For example, mud ob- Thus, with respect to the ethers of ethylene and propylene glycol there may be used, for example, the di v methyl diether of ethylene glycol (1,2-dimethoxy ethane), the mixed methyl, ethyl diether of ethylene glycol, and the dimethyl diether of propylene glycol.

Polyethylene glycols having the proper ratio of carbon to oxygen for use in accordance with the present invention comprise polyethylene glycols having an average 1 molecular weight of about 150 to 3,000, including triethylene glycol, tetraethylene glycol, a polyethylene glycol having an average molecular weight of about 300, a polyethylene glycol having an average molecular Weight of about 600, a polyethylene glycol having an average molecular weightof about 1,000, a polyethylene glycol 7 oxygen.

tained from a drilling well in Lake Raccourci in Louisiana may be found entirely suitable. Likewise, I may employin my invention dried ground shale such as has been obtained from a well in West Cote Blanche Bay in southern Louisiana. To asuitable suspension of col' loidal clay of the type exemplified is added a suitable amount of starch and additive. The amount" of clayor molecular weight of about '90 to 3,000 and a ratioof carbon to oxygen of about 1.5 to 2 .7-, saidjadditivebeing taken from the group consisting of alkoxy ethers of b it is employed.

ethylene and propylene glycol, polyethylene and polypropyleneglycols, and alkoxy ethers of polyethylene; and polypropylene glycols, said'alkoxy radicals of saidethers containing'not more'than about 16 carbon atoms, said drilling mud contain'ing not: more thanlabout 1* pound of alkalimetal hydroxide per '42 gallon barrel of'mud.

It is to be noted that theadditiveto be used should.

have a proper molecular weight (i.e;, a molecular weight of 90 to 3,000) and should also have a-properratio of age molecular Weight of about 300, a polypropylene glycol having an average molecular Weight of about 600, etc.

A- Wide variety of ethers of polyethylene glycols may 7 be used which will have the proper ratio of carbon to Thus there may be used the dimethyl diether of diethylene glycol, the diethyl ether of diethylene glycol, the mixed methyl, ethyl diether of diethylene glycol, the mixed methyl n-propyl-diether of diethylene glycol, the mixed methyl, isopropyl-diether of diethylene glycol, etc. Ethers of triethylene glycol that may be used include the dimethyl diether of triethylene glycol, the diethyl diether of triethylene glycol, etc. Representative ethers of. tetraethylene glycol include, for example, the dimethyl diether of tetramethylene glycol, the diethyl diether of tetraethylene glycol, the mixed ethyl propyl-diether of tetraethylene glycol, etc. Representative of the ethers of a polyethylene glycol having an average molecular weight of about 600 or-more include the dimethyl diether, the diethyl diether, the di-n-propyl diether, the di-' isopropyl diether, the dibutyl diether, the dipentyl diether, the dihexyl diether, mixed diethers such as mixed methyl, ethyl diether, the mixed methyl, propyl diether, the mixed pentyL'butyl diether, the mixed hexyl, pentyl diether, etc. There may also be used the dimethyl diether of dipropylene glycol.

Mixtures of two or more additives of the above-describedjnature may also be used, if desired.

Generally speaking, satisfactory results are obtained through the use of about 1 to 15 pounds of starch and about 0.5 to 5 pounds of additive per 42 gallon barrel of mud. It is to be understood, of course, that the amount of starch and the amount of additive required to give the desired reduction in filtration loss from a suspension of finely divided solids in an aqueous saline llquidvehicle will vary with circumstances over a comparatively wide range, in that the amounts of starch and additive to be employed in a specific suspension ordispersion will'dep'end upon the characteristics of the material to be treated and the circumstances under which- The starch and additive may beincorporated into the saline drilling muclin any of the suitable manners known to those skilled in the art. As a specificexainple of the practice of theopresent invention it maybe desirable to employ aqueous solutions of starch and the additive. The solutions may then be incorporated with the aqueous dispersion or suspensionof the finely divided solids. If desired, the starch, oradditive, or both,- may be directly incorporated in undiluted form in any suitable manner.

When it is desired to reduce the filtration'rate of the drilling mud, the materials aforementioned or solutions thereof may be incorporated into the mud at any suitable point in the mud circulation system such as in the mud pit. In some situations it may be desirable to use a mixing device such as a cone and jetmixer or the equivalent thereof for incorporating the starch and additive into the drilling mud. v i

The present invention may also be considered .in connection with the following examples which are given by way'of illustration and whih are not intended as limitations on the scope of this invention. l

' EXAMPLE 1. in"

Representative drilling .IlllldS were. prepared by incorporating clay, in this instance acommercial'blend of crude native Texas bentonite (cr'ude calcium montmorillonite) with Wyoming bentonite (sodium.montmorillonite) and sodium carbonate into water having dissolved therein five Weight percent of salt; Thereiwas also incorporated into the drilling muds' l .weightpereent of starch.,"Portions of the thus prepared'drilling mudwereltes'ted for viscosity, initial gel strength and filtration rate. In addition, representative portions of the .drilling mud were modified. by the incorporation of about 1 percent by weight of a variety of additives including 1,2-dimethoxy gen of about 2.6 whereas polypropylene glycol of molecular weight 750 will have a ratio of carbon to oxygen of about 2.8, which is outside thescope of the present invention. 1' l EXAMPLE 2 p A representative drilling mud was prepared as in Example 1 with but one exception, namely, the addition of 0.5

rather than 1% of sodium carbonate. That isto say, av

mudcomposiitibn was prepared comprising 20 weight percent of the commercial clay of Example 1 in 80 weight percent of an aqueous saline medium containing 5 weight percent of dissolved salt with 0.5% of sodium carbonate and 1% of starch added to the suspension.

A portion of the thus prepared mud was tested for viscosity, gel strength and filtration rate. To other portions of the mud there was added-1, 2 and 4 pounds per barrel of polyethylene glycolvhaving an average molecular weight of 600 and the thus modified portions were likewise tested for viscosity, gel strength .and filtration rate. The results are set forth in Table II.

Table II.-Efiects of polyethylene glycol, mol. wt. 600, on properties of a salt-water mud containing V2 NaaCOa and 1 starch ethane (the dimethyl ether of ethylene glycol), dipropylene glycol, ethylene glycol, polyethylene glycols hav- A ing average molecular weights of about 200 and 600, figfi f Imtiamel, Film; respectively, dioxane, and polypropylene glycols having Composition ene Glycol Q qGrams tion B average molecular weights of about 400 and 750, respecx 2 19 3 3 3535, 3, 53 tively. The thus modified portions of the drilling mud -l were likewise tested for viscosity, gel strength and filtration rate. The results obtained are set forth in Table I. i 2% Table I.Efiects of additives on drilling mud i g g Viscosity API Filtra- From Table II it will be seen that the viscosity and a i Material Added FQ S ggi g? gel strength are not adversely afiected through the addi-i cps. stormer min. tion of various amounts of polyethylene glycol whereas the filtration rate was progressively reduced as the amount 32 25 39 4 40 of added polyethylene glycol was increased. 28 is 1710 a a2 20 37.9 I p 4 3 e g gggg g gggi fik: is 2 As another example, a dr1lhng mud composition was Polyethylene glycoh. l 2s 17 13.4 prepared containing 20 weight percent of the commercial plr gl gvtooo. 6 37.9 clay of Example 1, 80 weight percent of sea water (which NQneHIIIIIIIIIIII 25 I is 38.5 contained about 3.5 weightpercent of dissolved salt), 0.5 fi 60 0 percent of sodium carbonate and 1 percent of starch. One Polypropylene gl col, 58 70 2s. 2 portion of the thus prepared drilling mud was tested witha out modification and another portion of the drilling mud yethylene glycol, 32 17 11.9 Mol. Wt. 600. was tested after the addition thereto of about 2 pounds With respect to compositions 1 and 2 it will be noted,

that when starch alone was present in the drilling mud a filtration rate of about 39.4 ccs. in 30 minutes was obtained and that this' filtration rate was reduced by more than 50% through theaddition of 1,2-dimethoxy ethane (composition 2). K

, 1 'With respect to compositions 3 to 7, it will be noted that the drilling mud sample containing only starchhad a filtration rate of 37.9 ccs. in 30 minutes and that the addition of ethylene glycol- (composition 5) and dioxane (composition 7) did not materially alter the filtration rate. Ethylene glycol has a'molecular weight of about 62. It will be noted, however, that the additives of the present invention (the dipropylene glycolof composition '4 and the polyethyleneglycol of 200 average molecular weight of composition 6) caused a reduction infiltration rate of about5.0% or more.

: weight 400 will have an average ratio of carbon to oxyweight of about 600.

per barrel of polyethylene. glycol having an average in Table IH.

Table III.Efiects of poly thylene glycol, mol. wt. 600, on

' properties of a sea-water mud Arnount of Polyethyl- Filtration Composition ene Glycol Viscosity, Initial Gel, Rate,

of Mel. cps. grains cc. API Wt. 600: LbJBbl.

EXAMPLE 4 prepared containing 22 weight percent of the commercial clay of Example. 1 and 78 weight percent of an aqueous saline medium containing 5 weight percent of dissolved salt. One portion of the thus prepared composition was The results obtained are set forth tested without modificationand to other portions of the composition there was added 1, 2, 4 and 8 pounds per barrel, respectively, of .a polyethylene. glycol having an average molecular weight of 300. The added polyethylene glycol had no material eifect on filtration rate as is shown by the results that were obtained, which are set forth in Table IV.

Table ll".Efiects of polyethylene glycol,. mol. wt. 300, additions on properties of drilling muds in absence of starch As has been indicated, the drilling mud of the present invention should not contain more than about 1 pound of alkali metal hydroxide per 42 gallon barrel of mud. As an example, a drilling mud was prepared containing 20 weight percent of the commercial clay of Example 1,

80 weight percent of a saline medium containing about weight percent of dissolved salt, with about 0:5 percent of sodium carbonate and about 1 percent of starch added to the suspension. A portion of the thus prepared compo sition was tested without modification and variousamounts of sodium hydroxide and polyethylene glycol A 3. -;A drilling mud as in claim 2 wherein the ether isv tainable without the addition of polyethylene glycol. With respect to composition 30, it is seen that the addition of about 1 pound per barrel of sodium hydroxide caused a still further increase in the filtration rate, as comparedwith composition 29, thus indicating that the beneficial reduction of filtration rate obtained with. the additives of the present inventionis largely lost when more than about 1 pound per 42 gallon barrel of sodium hydroxide orother alkali metal hydroxide is present in the drilling mud.

The nature and objects of the present invention having been fully described and illustrated, what is claimed is:

. 1.,A drilling mud comprising at least 5 percent by weight, of finely divided solids in an. aqueous saline medium containing about 2 to 15 weight percent of dissolved salt to. which has been added from about 1 to 15 pounds of starch per 42 gallon barrel of mud and from about. 0.5 to 5 pounds, per 42 gallon barrel ofmud of an additive having an average molecular weight of about 90. to. 3,000. and'a ratioof'carbon to. oxygen of about 1.510 2.7, said additive being taken from the group consisting of alkoxy ethers of ethylene and propylene glycol, polyethylene and polypropylene glycols, and alkoxy ethers of polyethylene and polypropylene glycols, said alkoxy radicals of said ethers containing not more than about 6 carbon atoms, said drilling mud containing not more than about 1 pound. of alkali metal hydroxide per 42 gallon barrel of mud. 2. A drilling mud as in claim 1 wherein the additive is an alkoxy ether.

1,2-dimethoxy ethane. V

4. A drilling mud as in claim 1 wherein the additive is a polyethylene glycol.

5. YA drilling mud as in claim 4 wherein the polyethylene.

I glycol is a polyethylene glycol having an average molecuhaving an average molecular weight of about 300 were" added to other portions of the drilling mud which were then tested. The compositions prepared and results obtained are set forth in Table V.

Table V.-Efiects of NaOH and polyethylene glycol, mol.

wt. 300, additions to a drilling mud 1 Added as a aqueous solution.

From Table V it will be seen that the addition of 0.25, 0.5 and 1.0 pounds per barrel of sodium hydroxide (compositions 24 to 25, respectively) had no substan@ tial eiiect on the filtration rate as compared Withthe control composition 23. It will also be noted that'with respect to composition 27 with addition of ipounds per barrelof polyethylene glycol in the absence of sodium hydroxide caused about an percent'reduction in filtra tron rate. The addition of about 0.25 pound perib'arrel of sodium hydroxide (composition28) did not materially afiect filtrationrate and. with the addition of 0.5 pound. per barrel of sodium hydroxide (Composition 29)."the

results were still satisfactoryin that the filtrationlrate was) substantially materially .eaow the filtration rate oblar weight of about 200 to 600.

6 A drilling mud as in claim 1 wherein the additive is a polypropylene glycol.

'7. A drilling mud as in claim 6 wherein the poly-:

tools in which there is circulated in the well 'a Water.

based drilling mud containing at least about 5 percent by Weight of finely divided solids, said Water base containing about 2 to 15 percent of dissolved salt, a method of forming a filter cake on the wall ofsaid well to decrease the lossof Water into a permeable formation penetrated by said well which comprises incorporating into said drilling mud from about 1 to;15 pounds of starchper 42 gallon barrel of mud and from about.0.5 to 5 pounds per 42 gallon barrelof mud of anadditi-ve having an average molecular Weightof about to. 3,000 and a ratio of carbon to oxygen of about 1.5 to- 2 .7, said additive being taken from'thegroup consisting ofalkoXy ethers of ethylene and propylene glycol, poly:

ethylene and polypropylene glycols, and trlkoxy ethers of. polyethylene and polypropylene glycols, saidfllkOXYa radicals -of said ethers containing not more thanjabout 6 carbon atoms, said' drilling mud containingf not more than about 1 pound of alkali metal hydroxide 'per 42 I gallon barrel. of mud, said starch and said additive being incorpora-ted in;amounts sufficient to substantially lower the filtration rate of said mud andcontactingsaidwall.

10 wherein the ether is References Cited in the file of this patent UNITED STATES PATENTS Barnes July 30, 1940 Jones Feb. 3, 1942' Chapman May 7, 1946 Meadors Mar. 18, 1952 

1. A DRILLING AND COMPRISING AT LEAST 5 PERCENT BY WEIGHT OF FINELY DIVIDED SOLIDS IN AN AQUEOUS SALINE MEDIUM CONTAINING ABOUT 2 TO 15 WEIGHT PERCENT OF DISSOLVED SALT TO WHICH HAS BEEN ADDED FROM ABOUT 1 TO 15 POUNDS OF STARCH PER 42 GALLON BARREL OF MUD AND FROM ABOUT 0.5 TO 5 POUNDS PER 42 GALLON BARREL OF MUD OF AN ADDITIVE HAVING AN AVERAGE MOLECULAR WEIGHT OF ABOUT 90 TO 3,00 AND A RATIO OF CARBON TO OXYGEN OF ABOUT 1,5 TO 2.7, SAID ADDITIVE BEING TAKEN FROM THE GROUP CONSISTING OF ALKOXY ETHERS OF ETHYLENE AND PROPYLENE GLYCOL, POLYETHYLENE AND POLYPROPYLENE GLYCOLS, AND ALKOXY ETHERS OF POLYETHYLENE AND POLYPROPLENE GLYCOLS, SAID ALKOXY RADICALS OF SAID ETHERS CONTAINING NOT MORE THAN ABOUT 6 CARBONS ATOMS, AND DRILLING MUD CONTAINING NOT MORE THAN ABOUT 1 POUND OF ALKALI METAL HYDROXIDE PER 42 GALLON BARREL OF MUD. 